Method of laminating a structure with adhesive containing a photoreactor composition

ABSTRACT

A method of generating reactive species which includes exposing a photoreactor composition to radiation, in which the photoreactor composition comprises a wavelength-specific sensitizer associated with a reactive species-generating photoinitiator. Also described are methods of polymerizing unsaturated monomers and curing an unsaturated oligomer/monomer mixture.

TECHNICAL FIELD

The present invention relates to a composition and method for generatinga reactive species. The present invention more particularly relates to acomposition and method for generating reactive species which can be usedto polymerize or photocure polymerizable unsaturated material.

BACKGROUND OF THE INVENTION

The present invention relates to a method of generating a reactivespecies. The present invention also relates to radiation-initiatedpolymerization and curing processes. For convenience, much of thediscussion which follows centers on free radicals as a particularlysignificant reactive species. Such discussion, however, is not to beconstrued as limiting either the spirit or scope of the presentinvention.

Polymers long have served essential needs in society. For many years,these needs were filled by natural polymers. More recently, syntheticpolymers have played an increasingly greater role, particularly sincethe beginning of the 20th century. Especially useful polymers are thoseprepared by an addition polymerization mechanism, i.e., free radicalchain polymerization of unsaturated monomers, and include, by way ofexample only, coatings and adhesives. In fact, the majority ofcommercially significant processes is based on free-radical chemistry.That is, chain polymerization is initiated by a reactive species whichoften is a free radical. The source of the free radicals is termed aninitiator or photoinitiator .

Improvements in free radical chain polymerization have focused both onthe polymer being produced and the photoinitiator. Whether a particularunsaturated monomer can be converted to a polymer requires structural,thermodynamic, and kinetic feasibility. Even when all three exist,kinetic feasibility is achieved in many cases only with a specific typeof photoinitiator. Moreover, the photoinitiator can have a significanteffect on reaction rate which, in turn, may determine the commercialsuccess or failure of a particular polymerization process or product.

A free radical-generating photoinitiator may generate free radicals inseveral different ways. For example, the thermal, homolytic dissociationof an initiator typically directly yields two free radicals perinitiator molecule. A photoinitiator, i.e., an initiator which absorbslight energy, may produce free radicals by either of two pathways:

(1) the photoinitiator undergoes excitation by energy absorption withsubsequent decomposition into one or more radicals; or

(2) the photoinitiator undergoes excitation and the excited speciesinteracts with a second compound (by either energy transfer or a redoxreaction) to form free radicals from the latter and/or formercompound(s).

While any free radical chain polymerization process should avoid thepresence of species which may prematurely terminate the polymerizationreaction, prior photoinitiators present special problems. For example,absorption of the light by the reaction medium may limit the amount ofenergy available for absorption by the photoinitiator. Also, the oftencompetitive and complex kinetics involved may have an adverse effect onthe reaction rate. Moreover, commercially available radiation sources,such as medium and high pressure mercury and xenon lamps, emit over awide wavelength range, thus producing individual emission bands ofrelatively low intensity. Most photoinitiators only absorb over a smallportion of the emission spectra and, as a consequence, most of thelamps' radiation remains unused. In addition, most known photoinitiatorshave only moderate quantum yields (generally less than 0.4) at thesewavelengths, indicating that the conversion of light radiation toradical formation can be more efficient.

Thus, there are continuing opportunities for improvements in freeradical polymerization photoinitiators.

SUMMARY OF THE INVENTION

The present invention addresses some of the difficulties and problemsdiscussed above by the discovery of an efficient composition and methodfor utilizing radiation. Hence, the present invention comprehends acomposition and method for generating a reactive species which includesproviding a wavelength-specific sensitizer in association with areactive species-generating photoinitiator and irradiating thewavelength-specific sensitizer.

The association of a wavelength-specific sensitizer with a reactivespecies-generating photoinitiator results in a structure referred toherein for convenience as a photoreactor composition. One majoradvantage of the wavelength-specific sensitizers which make up thepresent invention is that they efficiently absorb radiation atwavelengths between approximately 250 nm and 350 nm.

The present method involves effectively tuning the energy-absorbingentity, referred to herein as a photoreactor composition, to efficientlyutilize an emitted band of radiation. The wavelength-specific sensitizereffectively absorbs photons and efficiently transfers the absorbedenergy to the photoinitiator which, in turn, generates a reactivespecies. The wavelength-specific sensitizer is adapted to have anabsorption peak generally corresponding to a maximum emission band ofthe radiation source.

As a result of the wavelength-specific sensitizer of the presentinvention absorbing radiation in the range of about 250 to 350nanometers, the photoreactor composition of the present invention willgenerate one or more reactive species upon exposure to sunlight.Accordingly, the photoreactor composition of the present inventionprovides a method for the generation of reactive species that does notrequire the presence of a particular light source.

The present invention also includes a method of polymerizing anunsaturated monomer by exposing the unsaturated monomer to radiation inthe presence of the efficacious photoreactor composition describedabove. When an unsaturated oligomer/monomer mixture is employed in placeof the unsaturated monomer, curing is accomplished.

The present invention further includes a film and a method for producinga film, by drawing an admixture of unsaturated polymerizable materialand the photoreactor composition of the present invention, into a filmand irradiating the film with an amount of radiation sufficient topolymerize the composition. When the unsaturated polymerizable materialis an unsaturated oligomer/monomer mixture, curing is accomplished. Theadmixture may be drawn into a film on a nonwoven web or on a fiber,thereby providing a polymer-coated nonwoven web or fiber, and a methodfor producing the same.

The present invention also includes an adhesive composition comprisingan unsaturated polymerizable material admixed with the photoreactorcomposition of the present invention. Similarly, the present inventionincludes a laminated structure comprising at least two layers bondedtogether with the above described adhesive composition, in which atleast one layer is a cellulosic or polyolefin nonwoven web or film.Accordingly, the present invention provides a method of laminating astructure wherein a structure having at least two layers with the abovedescribed adhesive composition between the layers is irradiated topolymerize the adhesive composition. When the unsaturated polymerizablematerial in the adhesive is an unsaturated oligomer/monomer mixture, theadhesive is irradiated to cure the composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of the excimer lamp employed inthe examples.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the unexpected discovery of anefficient reactive species-generating composition and methods forutilizing the same. More particularly, the present invention includes acomposition and method for generating a reactive species which includesproviding a wavelength-specific sensitizer in association with areactive species-generating photoinitiator and irradiating thewavelength-specific sensitizer. The association of a wavelength-specificsensitizer with a reactive species-generating photoinitiator results ina structure referred to herein for convenience as a photoreactorcomposition.

The present invention also comprehends a method of polymerizing anunsaturated polymerizable material by exposing the unsaturated materialto radiation in the presence of the efficacious photoreactor compositiondescribed above. Further, the present invention includes a film and amethod for producing a film, by drawing an admixture of unsaturatedpolymerizable material and the photoreactor composition of the presentinvention, into a film and irradiating the film with an amount ofradiation sufficient to polymerize the composition.

Also, the present invention includes an adhesive composition comprisingan unsaturated polymerizable material admixed with the photoreactorcomposition of the present invention. Similarly, the present inventionincludes a laminated structure comprising at least two layers bondedtogether with the above described adhesive composition, in which atleast one layer is a cellulosic or polyolefin nonwoven web or film.Accordingly, the present invention provides a method of laminating astructure wherein a structure having at least two layers with the abovedescribed adhesive composition between the layers is irradiated topolymerize the adhesive composition.

The photoreactor composition of the present invention will be describedin detail below, followed by a detailed description of the method ofgenerating reactive species, and the various representative applicationsof the method.

The photoreactor composition of the present invention is thewavelength-specific sensitizer associated with a reactivespecies-generating photoinitiator. Accordingly, the term "photoreactorcomposition" is used herein to mean a wavelength-specific sensitizerassociated with a reactive species-generating photoinitiator. In anembodiment where the sensitizer is admixed with the photoinitiator, theterm "photoreactor composition" is used to mean the admixture. In theembodiment where the sensitizer is covalently bonded to thephotoinitiator, the term "photoreactor composition" is used to mean theresultant molecule.

The term "associated" as used herein is meant to include any means whichresults in the wavelength-specific sensitizer and the reactivespecies-generating photoinitiator being in sufficiently close proximityto each other to permit the transfer of energy absorbed by thesensitizer to the photoinitiator. For example, the wavelength-specificsensitizer and the reactive species-generating photoinitiator may bebonded to each other or to a spacer molecular as described hereinafterby covalent, hydrogen, van der Waals, or ionic bonds. Alternatively, thesensitizer and the photoinitiator may be physically admixed.

The term "wavelength-specific sensitizer" is used herein to mean thatthe sensitizer is adapted to have an absorption wavelength bandgenerally corresponding to an emission peak of the radiation. Either orboth of the sensitizer and the radiation may have more than oneabsorption wavelength band and emission peak, respectively. In the eventboth the sensitizer and the radiation have more than one absorptionwavelength band and emission peak, respectively, the generalcorrespondence just described need not be limited to a single absorptionwavelength band and a single emission peak.

According to the present invention, the "wavelength-specific sensitizer"is an arylketoalkene wavelength-specific sensitizer having the followinggeneral formula: ##STR1## wherein R₁ is hydrogen, an alkyl, alkenyl,cycloalkyl, heterocycloalkyl, aryl or a heteroaryl group;

R₂ is hydrogen, alkyl, alkenyl, cycloalkyl, heterocycloalkyl, aryl or aheteroaryl group;

R₃ is hydrogen, alkyl, alkenyl, cycloalkyl, heterocycloalkyl, aryl or aheteroaryl group; and

R₄ is an aryl, heteroaryl, or substituted aryl group.

Desirably, the arylketoalkene sensitizer has the following formula:##STR2## which efficiently absorbs radiation having a wavelength atabout 308 nanometers, or ##STR3## which efficiently absorbs radiationhaving a wavelength at about 280 nanometers. Desirably, the sensitizerof the present invention is in the trans configuration with respect tothe double bond. However, the sensitizer may also be in the cisconfiguration across the double bond.

As stated above, the wavelength-specific sensitizer of the presentinvention may optionally be covalently bonded to the reactivespecies-generating photoinitiator. In that embodiment, the aryl group ofthe wavelength-specific sensitizer of the present invention can containa group including, but not limited to, a carboxylic acid group, analdehyde group, an amino group, a haloalkyl group, a hydroxyl group, ora thioalkyl group attached thereto to allow the arylketoalkene to becovalently bonded to the other molecule. Accordingly, the arylketoalkenesensitizer compound includes the following: ##STR4##

Although it is preferred that the group attached to the aryl group ispara to the remainder of the sensitizer molecule, the group may also beortho or meta to the remainder of the molecule.

The term "reactive species" is used herein to mean any chemicallyreactive species including, but not limited to, free-radicals, cations,anions, nitrenes, and carbenes. Illustrated below are examples ofseveral of such species. Examples of carbenes include, for example,methylene or carbene, dichlorocarbene, diphenylcarbene,alkylcarbonylcarbenes, siloxycarbenes, and dicarbenes. Examples ofnitrenes include, also by way of example, nitrene, alkyl nitrenes, andaryl nitrenes. Cations (sometimes referred to as carbocations orcarbonium ions) include, by way of illustration, primary, secondary, andtertiary alkyl carbocations, such as methyl cation, ethyl cation, propylcation, t-butyl cation, t-pentyl cation, t-hexyl cation; allyliccations; benzylic cations; aryl cations, such as triphenyl cation;cyclopropylmethyl cations; methoxymethyl cation; triarylsulphoniumcations; and acyl cations. Cations also include those formed fromvarious metal salts, such as tetra-n-butylammonium tetrahaloaurate(III)salts; sodium tetrachloroaurate(III); vanadium tetrachloride; andsilver, copper(I) and (II), and thallium(I) triflates. Examples ofanions (sometimes referred to as carbanions) include, by way of example,alkyl anions, such as ethyl anion, n-propyl anion, isobutyl anion, andneopentyl anion; cycloalkyl anions, such as cyclopropyl anion,cyclobutyl anion, and cyclopentyl anion; allylic anions; benzylicanions; aryl cations; and sulfur- or phosphorus-containing alkyl anions.Finally, examples of organometallic photoinitiators include titanocenes,fluorinated diaryltitanocenes, iron arene complexes, manganesedecacarbonyl, and methylcyclopentadienyl manganese tricarbonyl.Organometallic photoinitiators generally produce free radicals orcations.

Any reactive species-generating photoinitiator may be used whichgenerates the desired reactive species. With regard to the freeradical-generating photoinitiators, these photoinitiators may be any ofthe photoinitiators known to those having ordinary skill in the art. Thelargest group of photoinitiators are carbonyl compounds, such asketones, especially α-aromatic ketones. Examples of α-aromatic ketonephotoinitiators include, by way of illustration only, benzophenones;xanthones and thioxanthones; α-ketocoumarins; benzils;α-alkoxydeoxybenzoins; benzil ketals or α, α-dialkoxydeoxybenzoins;enzoyldialkylphosphonates; acetophenones, such as α-hydroxycyclohexylphenyl ketone, α,α-dimethyl-α-hydroxyacetophenone, α,α-dimethyl-α-morpholino-4-methylthio-acetophenone,α-ethyl-α-benzyl-α-dimethylaminoacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-morpholinoacetophenone,α-ethyl-α-benzyl-α-dimethylamino-3,4dimethoxyacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-methoxyacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-dimethylaminoacetophenone,α-ethyl-α-benzyl-α-dimethylamino-4-methylacetophenone,α-ethyl-α-(2-propenyl)-α-dimethylamino-4-morpholinoacetophenone,α,α-bis(2-propenyl)-α-dimethylamino-4-morpholinoacetophenone,α-methyl-α-benzyl-α-dimethylamino-4-morpholinoacetophenone, andα-methyl-α-(2-propenyl)-α-dimethylamino-4-morpholinoaceto-phenone;α,α-dialkoxyaceto-phenones; α-hydroxyalkylphenones; O-acyl α-oximinoketones; acylphosphine oxides; fluorenones, such as fluorenone,2-t-butylperoxycarbonyl-9-fluorenone,4-t-butylperoxyvarbonyl-nitro-9-fluorenone, and2,7-di-t-butylperoxy-carbonyl-9-fluorenone; and α- and β-naphthylcarbonyl compounds. Other free radical generating photoinitiatorsinclude, by way of illustration, triarylsilyl peroxides, such astriarylsilyl t-butyl peroxides; acylsilanes; and some organometalliccompounds. The free radical-generating initiator desirably will be anacetophenone.

The types of reactions that various reactive species enter into include,but are not limited to, addition reactions, including polymerizationreactions; abstraction reactions; rearrangement reactions; eliminationreactions, including decarboxylation reactions; oxidation-reduction(redox) reactions; substitution reactions; and conjugation/deconjugationreactions.

In the embodiment where the wavelength-specific sensitizer is bound tothe reactive species-generating photoinitiator, any suitable method thatis known in the art may be used to bond the sensitizer to thephotoinitiator. The choice of such method will depend on the functionalgroups present in the sensitizer and photoinitiator and is readily madeby those having ordinary skill in the art. Such bonding may beaccomplished by means of functional groups already present in themolecules to be bonded, by converting one or more functional groups toother functional groups, by attaching functional groups to themolecules, or through one or more spacer molecules.

Examples 1-3 herein describe methods of preparing the arylketoalkenesensitizer of the present invention and covalently bonding it to aphotoinitiator, namely DAROCUR 2959. The reaction described in Example 3may be used on any arylketoalkene sensitizer of the present inventionhaving a carboxylic acid functional group on R₁ or R₂, whichever is thearyl group. This reaction of any arylketoalkene sensitizer isrepresented by the formula below, wherein R₃ represents the remainder ofthe arylketoalkene sensitizer of the present invention, and wherein thecarboxylic acid group is attached to R₁ or R₂ : ##STR5##

Desirably, the photoreactor composition of the present invention isrepresented by the following formula: ##STR6## More desirably, thephotoreactor composition of the present invention is represented by thefollowing formulas: ##STR7##

It is to be understood that the above reaction is merely one method ofbinding the sensitizer of the present invention to a photoinitiator, andthat other methods known in the art may be used.

The term "spacer molecule" is used herein to mean any molecule whichaids in the bonding process. For example, a spacer molecule may assistin the bonding reaction by relieving steric hindrance. Alternatively, aspacer molecule may allow use of more reactive or more appropriatefunctional groups, depending upon the functional groups present in thesensitizer and photoinitiator. It is contemplated that a spacer moleculemay aid in the transfer of energy from the sensitizer to thephotoinitiator, by either allowing a more favorable conformation orproviding a more favorable energy transfer pathway.

As noted earlier, the wavelength-specific sensitizer is adapted to havean absorption wavelength band generally corresponding to an emissionpeak of the radiation. In addition, the wavelength-specific sensitizerwill have a high intensity of absorption. For example, thewavelength-specific sensitizer may have a molar extinction coefficientgreater than about 5,000 liters per mole per cm (1 mole⁻¹ cm⁻¹) at anabsorption maximum. As another example, the wavelength-specificsensitizer may have a molar extinction coefficient (absorptivity)greater than about 10,000 1 mole⁻¹ cm⁻¹. As a further example, thewavelength-specific sensitizer will have a molar extinction coefficientgreater than about 20,000 1 mole⁻¹ cm⁻¹.

The absorption characteristics of the wavelength-specific sensitizer arenot limited to a single wavelength band. Many compounds exhibit morethan one absorption wavelength band. Consequently, a wavelength-specificsensitizer may be adapted to absorb two or more wavelength bands ofradiation. Alternatively, two or more wavelength-specific sensitizersmay be associated with a reactive species-generating photoinitiator.Such two or more wavelength-specific sensitizers may absorb the samewavelength band or they may absorb two or more different wavelengthbands of radiation.

The method of the present invention involves generating a reactivespecies by exposing a photoreactor composition to radiation in which thephotoreactor composition includes a wavelength-specific sensitizerassociated with a reactive species-generating photoinitiator. In otherwords, the method involves providing a wavelength-specific sensitizer inassociation with a reactive species-generating photoinitiator andirradiating the wavelength-specific sensitizer.

The term "quantum yield" is used herein to indicate the efficiency of aphotochemical process. More particularly quantum yield is a measure ofthe probability that a particular molecule will absorb a quantum oflight during its interaction with a photon. The term expresses thenumber of photochemical events per photon absorbed. Thus, quantum yieldsmay vary from zero (no absorption) to 1.

The sensitizer absorbs photons having a specific wavelength andtransfers the absorbed energy to the photoinitiator which, in turn,generates a reactive species. However, the efficiency with which areactive species is generated is significantly greater than thatexperienced with the reactive species-generating photoinitiator alone.For example, the photoreactor composition desirably will have a quantumyield greater than about 0.5. More desirably, the quantum yield of thephotoreactor composition will be greater than about 0.6. Even moredesirably, the quantum yield of the photoreactor composition will begreater than about 0.7. Still more desirably, the quantum yield of thephotoreactor composition will be greater than about 0.8, with the mostdesirable quantum yield being greater than about 0.9.

The term "polymerization" is used herein to mean the combining, e.g.covalent bonding, of large numbers of smaller molecules, such asmonomers, to form very large molecules, i.e., macromolecules orpolymers. The monomers may be combined to form only linearmacromolecules or they may be combined to form three-dimensionalmacromolecules, commonly referred to as crosslinked polymers.

As used herein, the term "curing" means the polymerization of functionaloligomers and monomers, or even polymers, into a crosslinked polymernetwork. Thus, curing is the polymerization of unsaturated monomers oroligomers in the presence of crosslinking agents.

The terms "unsaturated monomer," "functional oligomer," and"crosslinking agent" are used herein with their usual meanings and arewell understood by those having ordinary skill in the art. The singularform of each is intended to include both the singular and the plural,i.e., one or more of each respective material.

The term "unsaturated polymerizable material" is meant to include anyunsaturated material capable of undergoing polymerization. The termencompasses unsaturated monomers, oligomers, and crosslinking agents.Again, the singular form of the term is intended to include both thesingular and the plural.

Exposing the photoreactor composition to radiation results in thegeneration of a reactive species. Thus, the photoreactor composition maybe employed in any situation where reactive species are required, suchas for the polymerization of an unsaturated monomer and the curing of anunsaturated oligomer/monomer mixture. The unsaturated monomers andoligomers may be any of those known to one having ordinary skill in theart. In addition, the polymerization and curing media also may containother materials as desired, such as pigments, extenders, aminesynergists, and such other additives as are well known to those havingordinary skill in the art.

By way of illustration only, examples of unsaturated monomers andoligomers include ethylene; propylene; vinyl chloride; isobutylene;styrene; isoprene; acrylonitrile; acrylic acid; methacylic acid; ethylacrylate; methyl methacrylate; vinyl acrylate; allyl methacrylate;tripropylene glycol diacrylate; trimethylol propane ethoxylate acrylate;epoxy acrylates, such as the reaction product of a bisphenol A epoxidewith acrylic acid; polyester acrylates, such as the reaction product ofacrylic acid with an adipic acid/ hexanediol-based polyester; urethaneacrylates, such as the reaction product of hydroxypropyl acrylate withdiphenylmethane-4,4'-diisocyanate; and polybutadiene diacrylateoligomer.

Accordingly, the present invention also comprehends a method ofpolymerizing an unsaturated monomer by exposing the unsaturated monomerto radiation in the presence of the efficacious photoreactor compositiondescribed above. When an unsaturated oligomer/monomer mixture isemployed in place of the unsaturated monomer, curing is accomplished. Itis to be understood that the polymerizable material admixed with thephotoreactor composition of the present invention is to be admixed bymeans known in the art, and that the mixture will be irradiated with anamount of radiation sufficient to polymerize the material. The amount ofradiation sufficient to polymerize the material is readily determinableby one of ordinary skill in the art, and depends upon the identity andamount of photoreactor composition, the identity and amount of thepolymerizable material, the intensity and wavelength of the radiation,and the duration of exposure to the radiation.

The present invention further includes a film and a method for producinga film, by drawing an admixture of unsaturated polymerizable materialand the photoreactor composition of the present invention, into a filmand irradiating the film with an amount of radiation sufficient topolymerize the composition. When the unsaturated polymerizable materialis an unsaturated oligomer/monomer mixture, curing is accomplished. Anyfilm thickness may be produced, as per the thickness of the admixtureformed, so long as the admixture sufficiently polymerizes upon exposureto radiation. The admixture may be drawn into a film on a nonwoven webor on a fiber, thereby providing a polymer-coated nonwoven web or fiber,and a method for producing the same. Any method known in the art ofdrawing the admixture into a film may be used in the present invention.The amount of radiation sufficient to polymerize the material is readilydeterminable by one of ordinary skill in the art, and depends upon theidentity and amount of photoreactor composition, the identity and amountof the polymerizable material, the thickness of the admixture, theintensity and wavelength of the radiation, and duration of exposure tothe radiation.

The term "fiber" as used herein denotes a threadlike structure. Thefibers used in the present invention may be any fibers known in the art.The term "nonwoven web" as used herein denotes a web-like mattercomprised of one or more overlapping or interconnected fibers in anonwoven manner. It is to be understood that any nonwoven fibers knownin the art may be used in the present invention.

The present invention also includes an adhesive composition comprisingan unsaturated polymerizable material admixed with the photoreactorcomposition of the present invention. Similarly, the present inventionincludes a laminated structure comprising at least two layers bondedtogether with the above described adhesive composition, in which atleast one layer is a cellulosic or polyolefin nonwoven web or film.Accordingly, the present invention provides a method of laminating astructure wherein a structure having at least two layers with the abovedescribed adhesive composition between the layers is irradiated topolymerize the adhesive composition. When the unsaturated polymerizablematerial in the adhesive is an unsaturated oligomer/monomer mixture, theadhesive is irradiated to cure the composition.

It is to be understood that any layers may be used in the presentinvention, on the condition that at least one of the layers allowssufficient radiation to penetrate through the layer to enable theadmixture to polymerize sufficiently. Accordingly, any cellulosic orpolyolefin nonwoven web or film known in the art may be used as one ofthe layers so long as they allow radiation to pass through. Again, theamount of radiation sufficient to polymerize the admixture is readilydeterminable by one of ordinary skill in the art, and depends upon theidentity and amount of photoreactor composition, the identity and amountof the polymerizable material, the thickness of the admixture, theidentity and thickness of the layer, the intensity and wavelength of theradiation, and the duration of exposure to the radiation.

The radiation to which the photoreactor composition is exposed generallywill have a wavelength of from about 4 to about 1,000 nanometers. Thus,the radiation may be ultraviolet radiation, including near ultravioletand far or vacuum ultraviolet radiation; visible radiation; and nearinfrared radiation. Desirably, the radiation will have a wavelength offrom about 100 to about 900 nanometers. More desirably, the radiationwill have a wavelength of from about 100 to 700 nanometers.

Desirably, when the reactive species-generating photoinitiator is anorganic compound, the radiation will be ultraviolet radiation having awavelength of from about 4 to about 400 nanometers. More desirably, theradiation will have a wavelength of from about 100 to about 375nanometers, and even more desirably will have a wavelength of from 200to about 370 nanometers. For example, the radiation may have awavelength of from about 222 to about 308 nanometers. The radiationdesirably will be incoherent, pulsed ultraviolet radiation from adielectric barrier discharge excimer lamp.

Excimers are unstable excited-state molecular complexes which occur onlyunder extreme conditions, such as those temporarily existing in specialtypes of gas discharge. Typical examples are the molecular bonds betweentwo rare gaseous atoms or between a rare gas atom and a halogen atom.Excimer complexes dissociate within less than a microsecond and, whilethey are dissociating, release their binding energy in the form ofultraviolet radiation. The dielectric barrier excimers in general emitin the range of from about 125 nm to about 500 nm, depending upon theexcimer gas mixture.

Dielectric barrier discharge excimer lamps (also referred to hereinafteras "excimer lamp") are described, for example, by U. Kogelschatz,"Silent discharges for the generation of ultraviolet and vacuumultraviolet excimer radiation." Pure & Appl. Chem., 62, No. 9, pp.16671674 (1990); and E. Eliasson and U. Kogelschatz, "UV ExcimerRadiation from Dielectric-Barrier Discharges." Appl. Phys. B. 46, pp.299-303 (1988). Excimer lamps were developed by ABB Infocom Ltd.,Lenzburg, Switzerland, and at the present time are available fromHeraeus Noblelight GmbH, Kleinostheim, Germany.

The excimer lamp emits incoherent, pulsed ultraviolet radiation. Suchradiation has a relatively narrow bandwidth, i.e., the half width is ofthe order of approximately 5 to 100 nanometers. Desirably, the radiationwill have a half width of the order of approximately 5 to 50 nanometers,and more desirably will have a half width of the order of 5 to 25nanometers. Most desirably, the half width will be of the order ofapproximately 5 to 15 nanometers.

The ultraviolet radiation emitted from an excimer lamp can be emitted ina plurality of wavelengths, wherein one or more of the wavelengthswithin the band are emitted at a maximum intensity. Accordingly, a plotof the wavelengths in the band against the intensity for each wavelengthin the band produces a bell curve. The "half width" of the range ofultraviolet radiation emitted by an excimer lamp is defined as the widthof the bell curve at 50% of the maximum height of the bell curve.

The emitted radiation of an excimer lamp is incoherent and pulsed, thefrequency of the pulses being dependent upon the frequency of thealternating current power supply which typically is in the range of fromabout 20 to about 300 kHz. An excimer lamp typically is identified orreferred to by the wavelength at which the maximum intensity of theradiation occurs, which convention is followed throughout thisspecification and the claims. Thus, in comparison with most othercommercially useful sources of ultraviolet radiation which typicallyemit over the entire ultraviolet spectrum and even into the visibleregion, excimer lamp radiation is essentially monochromatic.

As a result of the wavelength-specific sensitizer of the presentinvention absorbing radiation in the range of about 250 to about 350nanometers, and more particularly at about 270 to 320 nanometers, thephotoreactor composition of the present invention will generate one ormore reactive species upon exposure to sunlight. Accordingly, thephotoreactor composition of the present invention provides a method forthe generation of reactive species that does not require the presence ofa special light source. The photoreactor composition of the presentinvention enables the production of adhesive and coating compositionsthat consumers can apply to a desired object and polymerize or cure uponexposure to sunlight. The photoreactor composition of the presentinvention also enables numerous industry applications whereinunsaturated polymerizable materials may be polymerized merely uponexposure to sunlight. Therefore, the photoreactor composition of thepresent invention will eliminate the cost of purchasing and maintaininglight sources in numerous industries wherein such light sources arenecessary without the photoreactor composition of the present invention.

As shown in the Examples below, the superiority of the photoreactorcompositions of the present invention over known photoinitiators isclear, even when the radiation is not the essentially monochromaticemission. The effective tuning of the photoreactor composition for aspecific wavelength band permits the photoreactor composition to moreefficiently utilize the target radiation in the emission spectrum of theradiating source corresponding to the "tuned" wavelength band, eventhough the intensity of such radiation may be much lower than, forexample, radiation from a narrow band emitter, such as an excimer lamp.In other words, the effectiveness of the radiation transorbercomposition of the present invention is not necessarily dependent uponthe availability or use of a narrow wavelength band radiation source.

Also, as shown in Example 4, the photoreactor composition of the presentinvention is exceptionally efficient. In Example 4, a mixture of Genomer1500B with a concentration of only about 0.5% of the photoreactorcomposition produced in Example 3 was totally cured upon exposure to theexcimer lamp. The concentration of photoreactor composition used inExample 4 is substantially lower than the amounts normally used in theprior art. Typical concentrations of conventional photoreactors in theprior art are between approximately 2% to 20% by weight.

The present invention is further described by the examples which follow.Such examples, however, are not to be construed as limiting in any wayeither the spirit or the scope of the present invention. In theexamples, all parts are by weight, unless stated otherwise.

EXAMPLE 1

This example describes a method of synthesizing the followingwavelength-specific sensitizer: ##STR8##

The wavelength-specific sensitizer is produced as summarized below:##STR9##

To a 250 ml round bottom flask fitted with a magnetic stir bar, and acondenser, was added 10.8 g (0.27 mole) sodium hydroxide (Aldrich), 98 gwater and 50 g ethanol. The solution was stirred while being cooled toroom temperature in an ice bath. To the stirred solution was added 25.8g (0.21 mole) acetophenone (Aldrich) and then 32.2 g (0.21 mole)4-carboxybenzaldehyde (Aldrich). The reaction mixture was stirred atroom temperature for approximately 8 hours. The reaction mixturetemperature was checked in order to prevent it from exceeding 30° C.Next, dilute HCl was added to bring the mixture to neutral pH asindicated by universal pH indicator paper. The white/yellow precipitatewas filtered using a Buchner funnel to yield 40.0 g (75%) after dryingon a rotary pump for four hours. The product was used below withoutfurther purification.

The resulting reaction product had the following physical parameters:

Mass. Spec. m/e (m⁺) 252, 207, 179, 157, 105, 77, 51.

The ultraviolet radiation spectrum of the product had an extinctioncoefficient of about 24,000 at about 304 nanometers, and λ_(max) was at308 nanometers.

EXAMPLE 2

This example describes a method of making the followingwavelength-selective sensitizer, namely 4- 4'-carboxyphenyl!-3-buten-2-one: ##STR10##

The wavelength-specific sensitizer was produced as summarized below:##STR11##

The method of Example 1 was followed except that acetone (Fisher, OptimaGrade) was added first, and then the carboxybenzaldehyde was added. Moreparticularly, 32.2 (0.21 mole) of carboxybenzaldehyde was reacted with12.2 g (0.21 mole) of acetone in the sodium hydroxide/ethanol/watermixture described in Example 1. Dilute HCl was added to bring thereaction mixture to neutral pH, yielding 37.1 g (91%) of a pale yellowpowder which was used without further purification in the followingexamples.

The resulting reaction product, namely 4- 4'-carboxyphenyl!-3-buten-2-one, had the following physical parameters:

Mass. Spec. 190 (m⁺), 175, 120.

EXAMPLE 3

This example describes a method of covalently bonding the compoundproduced in Example 1 to a photoreactor, namely DAROCUR 2959, as issummarized below: ##STR12##

To a 500 ml round bottom flask fitted with a magnetic stir bar, andcondenser, was placed 20 g (0.08 mole) of the composition prepared inExample 1, 17.8 g (0.08 mole) DAROCUR 2959 (Ciba-Geigy, N.Y.), 0.5 gp-toluenesulfonic acid (Aldrich), and 300 ml anhydrous benzene(Aldrich). The Dean and Stark adapter was put on the flask and thereaction mixture heated at reflux for 8 hours after which point 1.5 mlof water had been collected (theo. 1.43 ml). The reaction mixture wasthen cooled and the solvent removed on a rotary evaporator to yield 35.4g. The crude product was recrystalized from 30% ethyl acetate in hexaneto yield 34.2 g (94%) of a white powder. The resulting reaction producthad the following physical parameters:

Mass. Spectrum: 458 (m⁺), 440, 399, 322, 284.

EXAMPLE 4

The following experiment tested the curing ability of the compoundproduced in Example 3. More particularly, the compound produced inExample 3 was mixed with the difunctional alkyl urethane acrylateadhesive Genomer® 1500B (Mader, Biddle Sawyer Corporation, New York,N.Y.) and exposed to a 308 nm excimer lamp on a conveyor belt. Twoformulations were studied:

Formulation I

About 0.05 g of the compound produced in Example 3 was mixed with 10 gof Genomer® 1500B. Therefore the concentration of the compound producedin Example 3 in the mixture was about 0.5%. These components were mixedby means of a magnetic stirring bar at 80° C. A few drops of the mixturewas placed on a heated metal plate (Q-Panel Company, Westlake, Ohio) anddrawn down to a thickness of about 0.1 mm by means of a 0 draw-down bar(Industry Tech., Oldsmar, Fla.).

Formulation II

About 0.025 g of DAROCUR 2959 was mixed with 10 g of GENOMER 1500B.These components were mixed and then drawn out on heated metal plateswith a 0 draw-down bar as per Formulation I.

Each plate was then exposed to a 308 nanometer excimer lamp on aconveyor belt for approximately 0.8 seconds. The conveyor belt was setat 50 feet/minute. The plate having Formulation I thereon was totallycured upon exposure to the excimer lamp. In contrast, the plate havingFormulation II thereon remained tacky and was not fully cured.

EXAMPLE 5

This example describes the evaluation of the curing behavior of anadhesive containing the photoreactor compositions of Example 3 asreported in Example 4 upon exposure to ultraviolet radiation from anexcimer lamp.

An excimer lamp configured substantially as described by Kozelschatz andEliasson et al., supra, was employed and is shown diagrammatically inFIG. 1. With reference to FIG. 1, the excimer lamp 100 consisted ofthree coaxial quartz cylinders and two coaxial electrodes. The outercoaxial quartz cylinder 102 was fused at the ends thereof to a centralcoaxial quartz cylinder 104 to form an annular discharge space 106. Anexcimer-forming gas mixture was enclosed in the annular discharge space106. An inner coaxial quartz cylinder 108 was placed within the centralcylinder 104. The inner coaxial electrode 110 consisted of a wire woundaround the inner cylinder 108. The outer coaxial electrode 112 consistedof a wire mesh having a plurality of openings 114. The inner coaxialelectrode 110 and outer coaxial electrode 112 were connected to a highvoltage generator 116. Electrical discharge was maintained by applyingan alternating high voltage to the coaxial electrodes 110 and 112. Theoperating frequency was 40 kHz, the operating voltage 10 kV. Coolingwater was passed through the inner coaxial quartz cylinder 108, therebymaintaining the temperature at the outer surface of the lamp at lessthan about 120° C. The resulting ultraviolet radiation was emittedthrough the openings 114 as shown by lines 118. The lamp was used as anassembly of four lamps 100 mounted side-by-side in a parallelarrangement.

A film of adhesive was deemed cured completely, i.e., through the entirethickness of the film, when it passed the scratch test; see, e.g., M.Braithwaite et al., "Chemistry & Technology of UV & EB Formulation forCoatings, Inks & Paints," Vol. IV, SITA Technology Ltd., London, 1991,pp. 11-12.

While the specification has been described in detail with respect tospecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

What is claimed is:
 1. A method of laminating a structure,comprising:providing a structure comprising at least two layers and anadhesive composition between said layers, herein at least one layer is acellulosic or polyolefin nonwoven web or film; and irradiating thestructure to polymerize the adhesive composition, wherein the adhesivecomposition comprises a wavelength-specific sensitizer associated with areactive species-generating photoinitiator, and an unsaturatedpolymerizable material, the sensitizer being represented by one of thefollowing formulae: ##STR13##
 2. The method of claim 1, wherein thereactive species-generating photoinitiator generates a reactive species.3. The method of claim 1, wherein the photoinitiator comprises abenzophenone, a xanthone, a thioxanthone, an acetophenone, a benzil, anacylphosphine oxide, a fluorenone, a naphthyl carbonyl compound, atriarylsilyl peroxide or an acylsilane.
 4. The method of claim 3,wherein the photoinitiator comprises an acetophenone.
 5. The method ofclaim 1, wherein the sensitizer absorbs radiation in a range of about250 to about 350 nanometers.
 6. A method of laminating at least twolayers comprising:providing at least two layers and an adhesivecomposition between the layers, wherein at least one layer is a nonwovenweb or film of cellulosic or polyolefin material; and irradiating theadhesive composition to polymerize the adhesive composition, wherein theadhesive composition comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator, andan unsaturated polymerizable material, the sensitizer being representedby one of the following formulae: ##STR14## the sensitizer beingcovalently bonded to the photoinitiator by a substitution reaction atthe carboxylic acid of the sensitizer.
 7. The method of claim 6, whereinthe reactive species-generating photoinitiator generates a reactivespecies.
 8. The method of claim 6, wherein the photoinitiator comprisesa benzophenone, a xanthone, a thioxanthone, an acetophenone, a benzil,an acylphosphine oxide, a fluorenone, a naphthyl carbonyl compound, atriarylsilyl peroxide or an acylsilane.
 9. The method of claim 8,wherein the photoinitiator comprises an acetophenone.
 10. The method ofclaim 6, wherein the sensitizer absorbs radiation in a range of about250 to about 350 nanometers.
 11. A method of laminating at least twolayers comprising:providing at least two layers and an adhesivecomposition between the layers, wherein at least one layer is a nonwovenweb or film of cellulosic or polyolefin material; and irradiating theadhesive composition to polymerize the adhesive composition, wherein theadhesive composition comprises a wavelength-specific sensitizercovalently bonded to a reactive species-generating photoinitiator, andan unsaturated polymerizable material, wherein the wavelength-specificsensitizer covalently bonded to the reactive species-generatingphotoinitiator is represented by one of the following formulae:##STR15##
 12. The method of claim 11, wherein the reactivespecies-generating photoinitiator generates a reactive species.
 13. Themethod of claim 11, wherein the sensitizer absorbs radiation in a rangeof about 250 to about 350 nanometers.
 14. The method of claim 11,wherein the wavelength-specific sensitizer bonded to the reactivespecies-generating photoinitiator is represented by the followingformula ##STR16##
 15. The method of claim 11, wherein thewavelength-specific sensitizer bonded to the reactive species-generatinginitiator is represented by the following formula ##STR17##